Personal computers can be connected to an optical disc drive to read data from a disc, such as a digital video disc (DVD). On the disc, data is typically stored in the form of pits and lands patterned in a radial track. The track is formed as a spiral extending from the inner edge of the disc to its outer edge. A pit is a location in the track where data have been recorded by creating a depression in the surface of the disc with respect to the lands. The lands are the areas between the pits in the tangential direction. The reflectivity of the pits is less than the reflectivity of the lands. To store audio or digital information, the length of the pits and lands are controlled according to a predefined encoding format.
Some DVDs have two general areas: a main storage area and a burst cutting area. In the main storage area, information is written on predetermined regions of the spiral track. DVDs can store any one or a combination of video, audio and data signals in the main storage area In the burst cutting area (BCA), located near the disc hub, a code (the so-called BCA code) is written. The BCA code typically stores disc identification information (e.g., serial number of the disc, title of the disc, etc.). Generally, disc identification information is recorded in the BCA after completion of the disc manufacturing process by a high-power system, such as a laser system. The BCA can store code of about twelve to 188 bytes in size and in 16-byte increments. BCA code is usually arranged in a series of low reflectance stripes arranged in the circumferential direction. Each stripe generally extends fully along the radial direction of the BCA.
According to current industry standards, the BCA is located between 22.3(+0/−0.4)mm and 23.50±0.05 mm from the center of the center hole of the disc. Further, the starting diameter of the lead-in area should not exceed 44.5 mm when the BCA code is applied. Under current standards, BCA code generally should includes a BCA preamble field, a BCA data field and a BCA postamble field. All of these fields are written continuously without gaps. The BCA preamble field should include 4 preamble bytes preceded by a BCA-sync-byte. The BCA data field should include information data, 4 bytes of error detection code and 16 bytes of error correction code, in the stated order. The size of the information data is approximately 16 n-4 bytes, where the variable “n” in the information data is a positive integer not greater than 12. The 4-byte error detection code should be attached to information data. A Reed-Soloman type error correction code (“ECC”) with 4-way interleave should be adopted for the information data and the BCA error detection code. Reed-Soloman is a well known method for error correction. A BCA-Resync is inserted before every 4 bytes throughout the data field. The BCA postamble field includes 4 postamble bytes preceded and followed by BCA-Resync.
When reading information from the main storage area of an optical disc, light from a laser beam is directed onto the track and the light beam is reflected back to a photo-sensor, such as a photo-diode. Because the pits and lands exhibit different reflectivity, the amount of reflected light changes at the transitions between the pits and the lands. In other words, the encoded pattern of the pits and lands modulates the reflected light beam. The photo-sensor receives the reflected light beam, and outputs a modulated signal, typically referred to as an RF signal, that is proportional to the energy of the light in the reflected light beam. FIG. 1 illustrates the relationship between the RF signal and the pits and lands. In particular, smaller pits or lands decrease both the period and the amplitude of the RF signal. In addition, the polarity of the RF signal changes when going from pits to lands and vice versa.
When reading data from the main storage area of a DVD disc, a search is performed to position an optical head assembly over a target region of the spiral track. To keep the optical head assembly properly positioned over the spiral track in the main storage area, electronic control circuitry generates a track error signal from the light reflected from the spiral track to the photo-sensor. However, in the burst cutting area, there is no track error signal to control the positioning of the optical head assembly. Thus, it is desirable to provide methods and apparatus to efficiently reach the burst cutting area and read the BCA code contained therein.